. DARWIN ON THE MOVEMENTS OF PLANTS. 501 



A stick cut in the shape of Fig. 3 was purposely split at the short 

 end, the split reaching heyond the hole. As the "wood was highly 



Fig. 3. Outline op Piece op Stick (reduced to one half natural size), with a hole through which 

 the radicle of a bean grew. Thickness of stick at uarro w end, -08 inch ; at broad end, -10. Depth 

 of hole, '1 inch. 



elastic, the split closed as soon as it was made. The stick and bean 

 were buried in damp sand, the bean being placed so that the radicle in 

 growing would enter this hole. After six days they were dug up, and 

 the radicle was found much enlarged above and beneath the hole. The 

 fissure was open to a width of four millimetres, but as soon as the radi- 

 cle was removed it closed to two m.m. The stick was then suspended 

 horizontally by a fine wire passing through the hole, and a little saucer 

 was suspended beneath it to receive the weights, and it required eight 

 pounds eight ounces to open the fissure to the width of four m.m. 



Again, " holes were bored near the narrow end of two wooden clips 

 or pincers (Fig. 4), kept closed by brass spiral springs. Two radicles 

 in damp sand were allowed to grow through 

 these holes. The pincers rested on glass plates, 

 to lessen the friction from the sand. The holes 

 were a little larger and considerably deeper 

 than in the trials with the sticks, so that a 

 greater length of a rather thicker radicle exert- 

 ed a transverse strain. After thirteen days 

 they were taken up. The distance of two dots 

 (see Fig. 4) on the longer ends of the pincers 

 was now carefully measured ; the radicles were 

 then extracted from the holes, and the pincers 

 of course closed. They were then suspended 

 in the same way as the stick, and a weight of 

 three pounds four ounces was necessary with 

 one of the pincers to open them as much as the 

 radicle had done by transverse growth." This 

 radicle had escaped beyond the hole, and flat- 

 tened a little, as soon as it had slightly opened 

 the pincers, which had somewhat lessened 

 the strain. As a result of all his observa- Fig.4.Wooden pincers, kept 



,. , I -, rni ft,,- ' CLOSED BY A BRASS SPIRAL 



tions, lie concludes : 1 he radicle " increases in spring, with a hole (m inch 



1 xu 'iU 1 i ii f . ^^ diameter and -6 inch in 



length witn a lorce equal to the pressure oi at depth) bored through the 



1 , , c T T 1 . narrow closed part, through 



least a quarter ot a pound, and much greater which a radicle of a bean was 

 when prevented from bending" ; and "it in- tueTIo"^V-Fahr. '^''P"^' 

 creases in thickness, pushing away the damp 



earth on all sides with a force of above eight pounds in one case and 

 three pounds in another." 



